Can the Pope grant a special dispensation so a dying person goes straight to heaven, avoiding purgatory?

Of course, a Pope can give a dispensation. That's what an indulgence is. Whether he will or not, that's another story. The Church has already stipulated what the avenues are to receive an indulgence. Normally, you have to go through those. If there's a reason, the Pope could give a special dispensation. Yes, he could do that. Remember what Jesus said: I give you the keys of the kingdom. Whatever you bind is bound, whatever you loose is loosed. Couldn't be clearer.